Video tape cassettes for recording television pictures are accommodated and packaged in cases for purposes such as protection, labeling particulars, and decoration. Such a case for packaging a cassette is ordinarily made into a product by blanking or cutting out into a prescribed shape a relatively thick sheet material such as cardboard, boxboard, or plastic sheet as folding-in crease lines are formed therein thereby to form a blank sheet, folding this blank sheet in the shape of a case, and bonding together with an adhesive the overlapping portions of the side panels. A cassette is then inserted into this case and packaged to be distributed and used.
By a process of packaging into a case as described above, the formed case assumes a large volume in comparison with the state of the blank sheet, and it not only is disadvantageous in storing and transporting but also requires a work process wherein the cassette is inserted into and accommodated within the case and is accompanied by problems such as the requirement of an unexpected work time occasionally in instances wherein a case does not fit the cassette.
Ordinarily, when a case is formed by using a material such as a sheet of thermoplastic material such as polypropylene, polyethylene, or polystyrene or a laminated material including a paper or some other core sheet having on the surfaces thereof layers of these plastics, the overlapping parts of the side panels of the case are being bonded together by the measure of pressing them together under heating or of imparting ultrasonic or supersonic waves or high-frequency waves to them under pressure, but in this procedure it is necessary to insert a backup plate into the case, and forming of the case in a state wherein a cassette is accommodated therein cannot be carried out. Consequently, the forming productivity of the case forming process is of low efficiency of the order of 30 cases/minute, at the most, attendant upon the operation of inserting and extracting the backup plate.
Accordingly, in order to carry out with high efficiency the forming of the case in a state wherein a cassette is accommodated therein, there has been proposed means for injecting hot air between the opposed surfaces of the side panels to be overlapped thereby to instantaneously heat only the surface layers of the opposed surfaces of the side panels and to cause them to be fusion bondable or weldable, and immediately contact bonding the same, but with a conventional case, because of its construction described in detail hereinafter, this hot air infiltrates into the case interior and gives rise to problems such as heat deformation and deterioration of the accommodated cassette, and for this reason, this proposal has been one which was impossible to realize in practice.